Controlled gap carbon seals and multiple-tooth labyrinth seals are but two distinct and independent seals which exist and which are used to provide fluid seals around rotating shafts, particularly those in high temperature environments such as in gas turbine engines. In certain applications, double seals are employed, in which two seals, such as a double carbon seal for example, are disposed side-by-side.
Controlled gap carbon seals provide relatively good sealing capabilities due to the relatively small clearances which can be maintained between the carbon ring seal and an inner runner, such as a rotating shaft of a gas turbine engine for example. Such tight shaft clearances are possible due to the ability of the carbon ring seal to radially “float” relatively to the rotating shaft, which eliminates any possible eccentricity of the rotating shaft.
Multiple-tooth labyrinth seals are commonly employed for sealing rotating shafts in gas turbine engines due to their sealing effectiveness. However, labyrinth seals are more affected by shaft eccentricities and thermal expansion, and therefore are less effective at maintaining a small gap between the shaft and the seal structure.
Accordingly, an improved shaft seal is sought.